Crankshaft bearing arrangement of a combustion engine

ABSTRACT

The present disclosure refers to a crankshaft bearing arrangement for an internal combustion engine. The bearing arrangement comprises: a bearing arranged at a crankshaft of an internal combustion engine; a bearing seat for housing the bearing; and a sealing arrangement for sealing against the crankshaft and the bearing seat. The at least one part of the bearing seat has a reinforcement arranged in the bearing seat, and a surface of the at least one part of the bearing seat, which surface bears against the bearing, is made from a plastic material.

TECHNICAL FIELD

The present disclosure relates to a crankshaft bearing arrangement of acombustion engine, and, more specifically, to a crankshaft bearingarrangement of an internal combustion engine of a hand-held motor-driventool.

BACKGROUND

In the development of combustion engines for motor-driven tools, such aschainsaws, hedge trimmers, grass trimmers etc., bearing sleeves havebeen used to eliminate the need for after-treatment of bearing seats ofcrankshaft bearings after the bearings seats have been manufactured.

In U.S. Pat. No. 4,974,973 and WO97/45649, crankshaft bearingarrangements have been described using such bearing sleeves. In thebearing arrangement of, for example, U.S. Pat. No. 4,974,973, a bearingcan be arranged in a bearing sleeve, which is formed as a tin cup with arubber coated outer periphery. The rubber coated outer periphery isarranged to compensate for tolerances, e.g. size variations in theproduction of bearing seats and to seal against the cylinder and thecrankcase. Also, the arrangement has an internal periphery provided witha sealing ring to seal against the crankshaft.

Even if such arrangements have a lot of advantages, some exemplaryproblems may occur as follows:

-   -   Due to the rather large tolerances in such an arrangement, there        is a risk that the bearing is either too loosely arranged in the        sleeve, with a result that the bearing may rotate in the bearing        sleeve or that the bearing including the bearing sleeve will        rotate in the bearing seat, or that the bearing will press too        hard in the sleeve, risking obliqueness of the bearing or that        the bearing and/or the bearing sleeve is squeezed in the bearing        seat such that the bearing and/or the bearing sleeve finally        breaks.    -   Even if dimensions are achieved for which a proper squeezing of        the bearing and the bearing sleeve is achieved, it may be        difficult to seal such an arrangement. As a result, it may be        necessary to seal during operation with a substantial amount of        silicone glue between the bearing seat and bearing sleeve.

Also, such a solution is rather expensive to produce, since an expensivekind of rubber is usually used for the rubber-coated outer periphery.

SUMMARY

An object of the present disclosure is to create an improved crankshaftbearing arrangement which solves the above-mentioned problems.

This is solved by a crankshaft bearing arrangement disclosed herein.

According to a first embodiment, a crankshaft bearing arrangement isarranged such that at least one part of the bearing seat has areinforcement arranged in the bearing seat, and a surface of the atleast one part of the bearing seat, which bears against the bearing, ismade of a plastic material. The bearing arrangement also has a sealingarrangement for sealing against the crankshaft and bearing seat.

By having such a reinforcement, it would be possible to use a plasticmaterial for the surface of the bearing seat without risking acompression set in the plastic material. Another advantage compared tothe prior art solutions using a tin cup as a bearing sleeve, is thatsuch a bearing sleeve can be omitted in this solution, resulting insmaller tolerances between bearing seat and bearing, i.e., manufacturingsize variations. Still, existing construction tolerances can be receivedby the nature of the plastic material. Also, the plastic material can beproduced without after-treatment with a low tolerance compared to, e.g.,a metallic material. Therefore, with the arrangement according to theembodiment, there is low risk that the bearing is too loosely held inthe bearing seat, such that it may rotate or is too hardly held and istilted or damaged in any other way. Since the position between thebearing is well defined, a proper function of the crankshaft assemblyincluding piston rod, and good cooperation of crankshaft assembly andcylinder is ensured, which will result in good engine characteristicsand low emissions.

Another advantage with this arrangement is that the diameter of thebearing arrangement can be reduced since there is no bearing sleeve,which results in a more cost-effective arrangement. Also, when there isno bearing sleeve, the arrangement will be lighter and morecost-effective.

By arranging the surface of plastic material as a layer between thebearing and the reinforcement, the arrangement will be more resistant toloads, i.e., it may be exposed to rather high loads without risking acompression set in the plastic material. This is especially true if theplastic material is a fibre-reinforced plastic material.

In some embodiments, a cost-efficient sealing arrangement can be used,which can be produced from simple rubber materials and still achieve asatisfactory sealing against bearing seats and crankshaft. Also, such asealing arrangement can be produced as one unit at the time ofmanufacture.

By arranging the sealing arrangement such that it has at least oneprotrusion arranged in a pushing engagement with the bearing, tolerancesin the axial direction of the crankshaft can be received by theprotrusions.

By arranging the at least one protrusion of the sealing arrangement suchthat it bears against an outer ring of the bearing, a displacement canbe achieved between an outer ring and an inner ring of the bearing.Therefore, when the bearing is realized as a ball bearing, it is ensuredthat the balls of the ball bearing will be in contact with both theinner and the outer ring of the bearing. Due to this measure, thebearing will achieve a long life.

By arranging a number of protrusions forming a discontinuous ringbearing against an outer ring of the bearing, the sealing arrangementwill contribute to centering the bearing in an axial direction of thecrankshaft.

By arranging the at least one protrusion with a tapered shape, acompression that is proportional to the pressure from the bearing willbe achieved. Therefore, dimension variations in an axial direction dueto manufacturing tolerances can be well received independent of the sizeof the dimension variations.

According to a second aspect of the disclosure, an internal combustionengine is provided, comprising a crankshaft and at least one arrangementaccording to any of the embodiments described in this document.

According to third aspect of the disclosure, a hand-held motor-driventool is provided, comprising an internal combustion engine having acrankshaft and at least one arrangement according to any of theembodiments described in this document.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will in the following be described in more detail withreference to the enclosed drawings, wherein:

FIG. 1 illustrates an embodiment of a crankshaft bearing arrangement ina vertical cross-sectional view in an axial plane of a crankshaft atwhich a bearing arrangement is arranged.

FIG. 2 illustrates an embodiment of a crankshaft bearing arrangement ina vertical cross-sectional view in section I-I of FIG. 1.

FIG. 3 illustrates an enlargement of a part of FIG. 1 describing a partof a sealing arrangement according to an embodiment.

FIG. 4 illustrates a schematic front view of a side of a sealingarrangement facing the bearing, according to an embodiment.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments will be described more fully hereinafter withreference to the accompanying drawings. Other embodiments arecontemplated in many different forms and this disclosure should not beconstrued as limited to the embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the disclosure to thoseskilled in the art. In the drawings, like numbers refer to likeelements.

In the embodiments described in the figures, a crankshaft 16 is shown,which is journalled in two bearings 10, in the form of ball bearings.Although, other types of bearings might also be used. Between the twobearings 10, and mounted on the crankshaft is a crankshaft assembly 14with piston rod and counterweights. The bearings 10 are inserted in abearing seat, which in this embodiment, comprises an upper half 15,which is a lower part of a cylinder of an internal combustion engine,and a lower half 11, which is a part of a crankcase of a tool in whichthe arrangement is installed. Each bearing is supported by the twohalves of the bearing seat in such a way that the bearing seat housesthe bearings.

The lower half 11 of the bearing seat has a reinforcement 12 arranged asa layer of metal inside the bearing seat for receiving a pressure forcefrom each bearing. The reinforcement is coated by a plastic material,which provides a surface 13 of the lower half of the bearing seat, whichbears directly against the bearing. Therefore, the surface 13 of plasticmaterial is arranged as a layer between the bearing 10 and thereinforcement layer 12. The surface 13 is of a fibre-reinforced plasticmaterial, which can endure high loads and temperatures that may occur ina held-held motor-driven tool, such as a chainsaw. The surface is madeas thin as possible for the manufacturing process. Typically, when usingan injection casting procedure, the plastic surface 13 will be 1-1.5 mm.Typically, the reinforcement layer 12 has a thickness of approximately2-6 mm, depending, for example, on the size of the engine. The surfaceof plastic material bearing against the bearing may be made of the sameplastic material as the rest of the crankcase. Therefore, thereinforcement will be embedded in the plastic material of the crankcase,and the surface of the plastic material will be arranged as a layerbetween the bearing and the reinforcement. In the embodiment describedin the figures, the lower half of the bearing seat 11 has tworeinforcements, each arranged close to each bearing 10 as a metal layerinside the bearing seat.

In the embodiments described in the figures, see e.g., FIG. 2, thecylinder 15 rests on the upper part of the crankcase 11. For thisreason, the crankcase has an upper surface comprising four metal areas17, two at each bearing, on which the cylinder stands, called thecylinder foot plane. By arranging the plastic surface layer such that itextends to also cover the area around these four metal areas, there isno risk of leakage at the cylinder foot plane.

The embodiments described in the figures also shows two separate sealingarrangements 20, arranged against a side of each bearing 10, which facesaway from the crankshaft assembly 14, both sealing arrangements beingarranged around the crankshaft 16. Each sealing arrangement 20 isarranged as one unit to seal against the crankshaft 16 and the bearingseat 11, 15.

The sealing arrangement 20 shown in the embodiment described in thefigures is arranged as a sealing ring having a diameter substantiallyequal to the diameter of the bearing 10.

FIG. 4 shows a side of the sealing ring which, when the sealing ring isarranged on the crankshaft, faces the bearing 10. As can be seen inFIGS. 3 and 4, the sealing ring has a number of protrusions 21 arrangedat a certain radius of the ring such that the protrusions 21 bearagainst an outer ring of the bearing 10. Due to this measure, theprotrusions 21 help to push an outer ring of the bearing 10 in an axialdirection of the crankshaft 16 towards the crankshaft assembly 14, suchthat the bearings are pushed into a proper position, which results in along life for the bearings, the crankshaft assembly and the cylinder.The protrusions 21 preferably form a discontinuous ring bearing againstthe outer ring of the bearing 10. According to other embodiments, theprotrusions might also have other forms, such as a continuous ring.

The protrusions 21 preferably have a tapered shape in a directiontowards the outer ring of the bearing. Although, the protrusions 21might have other shapes, such as squared.

In the embodiment described above, the cylinder is manufactured from ametal, which means that it has a surface of metal bearing against thebearing 10. This surface has to be after-treated after the cylinder hasbeen produced in, for example, a die casting procedure to get lowtolerances and a fine surface against the bearing. Although, a cylinderof an internal combustion engine has to be after-treated anyhow,regarding other parts of a cylinder, and to make more after-treatment ofa part that anyhow experiences after-treatment is more cost-efficientthan to start an after-treatment process of a part that does not have tobe after-treated.

In the embodiment described, only the lower half of the bearing seat hasa plastic material surface bearing against the bearing and areinforcement arranged in the bearing seat close to the surface.Although, such an arrangement might also be used for an upper part ofthe bearing seat, or for parts of the lower or upper part of the bearingseat.

In the embodiment described, the bearing seat comprises a lower half ofa cylinder and an upper half of a crankcase, which are connected at ahorizontal section. In an alternative embodiment, the crankshaftarrangements in which a bearing seat is arranged coaxially onto acrankshaft as one integral part housing one bearing. In sucharrangements, the internal combustion engine comprises two bearingseats, one first bearing seat preferably housing a first bearing and onesecond bearing seat preferably housing a second bearing, arranged insuch a way that each bearing seat supports one respective bearing.Further, in this alternative embodiment the first bearing seat isintegrated in a first crankcase half and the second bearing seat isintegrated in a second crankcase half, wherein the two crankcase halvesare connected at a vertical section to form the crankcase. For sucharrangements, the whole or part of the surface of the bearing seat maybe coated with a plastic material, and correspondingly, the whole orpart of the bearing seat may have a reinforcement arranged in thebearing seat. If the reinforcement is arranged in the whole of onebearing seat, it may be arranged as a ring of, e.g., metal, arrangedclose to the surface of plastic material. Such a ring reinforcementwould be easy to manufacture and any after-treatment of a surfacebearing against the bearing would be unnecessary.

The plastic material of the surface of the bearing seat bearing againstthe bearing is preferably any kind of reinforced plastic material, suchas a carbon fibre reinforcement, a glass fibre reinforcement or anano-composite material. The surface may be of any kind of plasticmaterial that has a high heat distortion temperature. The higher theheat distortion temperature of the material and the thinner the layer ofplastic material, the less the plastic material will be deformed.

In the drawings and specification, there have been disclosed preferredembodiments and examples, although specific terms are employed, they areused in a generic and descriptive sense only and not for the purpose oflimitation, the scope of the disclosure being set forth in the followingclaims.

1-13. (canceled)
 14. A crankshaft bearing arrangement for an internalcombustion engine, said bearing arrangement comprising: a bearingarranged at a crankshaft of an internal combustion engine; a bearingseat for housing the bearing; and a sealing arrangement for sealingagainst the crankshaft and the bearing seat; wherein at least one partof the bearing seat has a reinforcement arranged in the bearing seat,and in that a surface of the at least one part of the bearing seat,which surface bears against the bearing, is made from a plasticmaterial.
 15. The crankshaft bearing arrangement according to claim 1,wherein the surface of plastic material is arranged as a layer betweenthe bearing and the reinforcement.
 16. The crankshaft bearingarrangement according to claim 1, wherein the reinforcement is made ofmetal.
 17. The crankshaft bearing arrangement according to claim 1,wherein the plastic material of the surface of the at least one part ofthe bearing seat is a fibre-reinforced plastic material capable ofstanding loads and temperatures that occur in an internal combustionengine of a hand-held motor-driven tool, such as a chainsaw.
 18. Thecrankshaft bearing arrangement according to claim 1, wherein the bearingseat comprises a lower half, and an upper half, and wherein thereinforcement is arranged in the lower half.
 19. The crankshaft bearingarrangement according to claim 1, wherein the bearing seat is arrangedas one integral part housing the bearing, and wherein the reinforcementis arranged in the whole of the bearing seat.
 20. The crankshaft bearingarrangement according to claim 1, wherein the sealing arrangement isarranged around the crankshaft and against a side of the bearing, whichside faces away from a crankshaft assembly, the sealing arrangementbeing arranged for sealing engagement with the crankshaft and thebearing seat.
 21. The crankshaft bearing arrangement according to claim7, wherein the sealing arrangement has at least one protrusion arrangedin a pushing engagement with the bearing, for pushing the bearing in anaxial direction of the crankshaft.
 22. The crankshaft bearingarrangement according to claim 8, wherein the at least one protrusion isarranged on the sealing arrangement such that it bears against an outerring of the bearing.
 23. The crankshaft bearing arrangement according toclaim 9, wherein the at least one protrusion comprises a number ofprotrusions forming a discontinuous ring bearing against the outer ringof the bearing.
 24. The crankshaft bearing arrangement according toclaim 9, wherein the at least one protrusion has a tapered shape in adirection towards the outer ring of the bearing.
 25. An internalcombustion engine comprising a crankshaft and at least one crankshaftbearing arrangement according to claim
 1. 26. The crankshaft bearingarrangement according to claim 1 wherein the crankshaft bearingarrangement is a component of a hand-held motor-driven tool.